A senior Defense Department official told U.S. lawmakers Wednesday that Americans have been killed by detainees who were released from the prison in Guantanamo Bay, Cuba.

Paul Lewis, the Pentagon's special envoy for closing the facility, declined to provide details, including whether the incidents occurred during the administration of President George W. Bush or President Barack Obama.

"What I can tell you is unfortunately there have been Americans that have died because of detainees," Lewis told the House Foreign Affairs Committee.

News agencies quoting unnamed officials have reported that the incident involved an Afghan prisoner released while Bush was president. There have also been allegations that a former detainee was involved in the attack on the U.S. Consulate in Benghazi, Libya, in 2012.

Guantanamo and Brussels

The disclosure came during a briefing by Defense and State department officials to lawmakers about how the prison has become a powerful propaganda tool for Islamic State. Obama and administration officials have said images of the U.S. detention facility are a reminder to the international community of U.S.-authorized torture and long-term detentions without trial.

"Countries across the world and allies tell us that Gitmo hurts us," Lewis said, using a shortened term for the Guantanamo facility. "By closing Gitmo, we address a concern of the rest of the world.”

But many Republican and some Democratic members of Congress have opposed closing Guantanamo.

Rep. Dana Rohrabacher, R-Calif., says that compared with the Guantanamo Bay detention center, "the bigger recruiting tool [for terrorists] is when our government, especially this administration, is perceived as being weak."

Representative Dana Rohrabacher, a California Republican, said Wednesday that European allies might change their negative opinions of the detention facility in the wake of the attacks that killed dozens and wounded hundreds more Tuesday in Belgium.

"Let me suggest that the attitude of our European friends may well be changing in the next six months or so when they realize that the slaughter that’s taking place in Paris and now in Brussels is part of an international movement to destroy Western civilization and replace it with a caliphate," he said.

FILE - Rep. Eliot Engel of New York, the ranking Democrat on the House Foreign Affairs Committee, calls Gitmo a "gift that keeps on giving" for extremists trying to recruit fighters.

The committee's ranking minority member, Representative Eliot Engel, a New York Democrat, called the facility a "gift that keeps on giving" for extremists trying to recruit fighters, but Rohrabacher said those concerns were misplaced.

"I think the bigger recruiting tool is when our government, especially this administration, is perceived as being weak," Rohrabacher said.

Transfers continue

More than 85 percent of those detained at Guantanamo Bay since 2002 have been transferred to other countries.

According to intelligence reporting, less than 5 percent of Gitmo detainees transferred during the Obama administration have returned to terrorism.

Some lawmakers, however, fear countries that have received Gitmo detainees, like Uruguay and Ghana, aren’t prepared to properly monitor them.

“Ghana’s a wonderful place. It’s a wonderful country. But the fact is, it does not have top-notch intelligence or law enforcement services to deal with this kind of problem,” Representative Ed Royce, a California Republican who serves as the committee's chairman, said Wednesday.

As more detainees become eligible for transfer, the Gitmo detention process remains hotly debated, but the option of moving detainees from Guantanamo to U.S. soil remains against the law.